This invention relates to a slide valve for pipelines, particularly hot-gas pipelines of large dimensions, comprising a valve housing intended to be built into the pipeline, a valve plate designed to be inserted into the valve housing and a seal provided between the valve plate and the valve housing, in which the sealing surfaces are displaceable relative to one another by at least one pressure-medium-operated bellows and at least one oppositely acting spring, for establishing and breaking a sealing contact.
In known slide valves of the type mentioned above, the arrangement is in every case such that, on receiving the pressure medium, the bellows (or compensator), seeks to establish sealing contact between the sealing surfaces, whilst the oppositely acting spring breaks the sealing contact when the supply of pressure medium to the bellows is interrupted.
An arrangement such as this is attended by significant disadvantages in cases where the slide valve is used for example in pipelines for transporting hot, dust-containing gases possibly laden with pollutants. This is because, in the event of a power failure affecting a slide valve of this type, the tensioned spring moves the sealing surfaces into a position in which the sealing contact is broken. The result of this is that hot gases can escape from the pipeline, which is a serious hazard, particularly in cases where the hot gases in question contain pollutants.